1. Field of the Invention
The present invention relates to an impact absorbing member and a vehicle bumper structure. More particularly, the present invention relates to an impact absorbing member for protecting the legs of a pedestrian from collision when being brought into collision with the pedestrian, and a vehicle bumper structure which uses the impact absorbing member.
2. Related Art
Conventionally, various types of impact absorbing members for mitigating an impact that is imparted to the leg portions of a pedestrian when a bumper portion of a running vehicle collide with the leg portions of the pedestrian and vehicle bumper structures using those impact absorbing members have been under development. In addition, many vehicles have been developed in recent years which have bumper structures in which bumpers which extend in widthwise directions of the vehicles are disposed in upper and lower positions in parallel at front and rear ends of vehicle bodies. In these vehicle having upper and lower parallel bumpers, various structures have been proposed which are designed to protect the leg portions of a pedestrian when the bumpers are brought into collision with the pedestrian.
For example, in a vehicle bumper structure described in JP-A-2002-274298, impact absorbing members are provided inside an upper bumper face and a lower bumper face, respectively, and the lower impact absorbing member is fixed to a vehicle body frame so as to increase the rigidity of the lower impact absorbing member higher than the rigidity of the upper impact absorbing member.
By adopting this configuration, at the time of collision, the upper impact absorbing member deforms plastically so as to absorb impact energy to protect the leg portions of a pedestrian. In addition, since the leg portions of the pedestrian are inclined rearwards of the vehicle body by the deformation of the upper impact absorbing member while lower portions of the leg portions of the pedestrian are carried upwards by the lower impact absorbing member which deforms less, the leg portions of the pedestrian can be protected safely in the collision.
In a vehicle bumper structure described in JP-A-2004-058726, a collapsing amount of the upper impact absorbing member is made to become larger than a collapsing amount of the lower impact absorbing member relative to the same load applied from the front of the vehicle body, and a ratio of these collapsing amounts is set to a predetermined value. By adopting this configuration, the leg portions, particularly, the knee portions of the pedestrian can be protected appropriately at the time of collision.
In addition, in a vehicle bumper structure described in JP-A-2004-276787, a vehicle bumper structure is proposed in which an upper bumper face is made to protrude further forwards than a lower bumper face. In this configuration, an upper impact absorbing member disposed inside the upper bumper face and a lower impact absorbing member disposed inside the lower bumper face are linked with each other by means of a link member.
Then, at the time of collision, the upper impact absorbing member moves rearwards while deforming according to a deformation in the upper bumper face which has been brought into abutment with upper portions of the knee portions of the pedestrian, while the lower impact absorbing member protrudes forwards by the action of the link member which is triggered by the rearward movement of the upper impact absorbing member to thereby come into forcible contact with lower portions of the knee portions of the pedestrian. This vehicle bumper structure protects the leg portions of the pedestrian in the same way as the vehicle bumper structures of JP-A-2002-274298 and JP-A-2004-058726 by guiding the upper portions of the leg portions and the upper body of the pedestrian to the rear of the vehicle body.
However, in the vehicle bumper structure described in JP-A-2004-276787, since the upper and lower impact absorbing members are connected together by the link member and are not fixed directly to a bumper beam or a vehicle body frame, when the vehicle collides with an obstacle other than pedestrians such as a vehicle, a guard rail or a wall, the link member is broken, and the impact absorbing capability of the bumper structure cannot necessarily be ensured to a sufficient level.
In addition, in this structure, the cross sectional area of the impact absorbing member has to be reduced to a small level due to a moving space having to be secured for the impact absorbing member. Because of this, there is caused a problem that the energy absorbing properties of the impact absorbing member cannot be increased enough.
In addition, in the vehicle bumper structures described in JP-A-2002-274298, JP-A-2004-058726 or JP-A-2004-276787, a case is anticipated in which the upper bumper face and the upper impact absorbing member collide with an upper or a lower portion of the knee portions of the legs of a pedestrian. However, with vehicles having a high overall height such as SUV's (Sport Utility Vehicles) which have been on the market in recent years, as is shown in FIG. 8, the height of an upper impact absorbing member 101 of a vehicle 100 becomes substantially the same as the height of the knee portions H of the leg portions L of a pedestrian, and at the time of collision, there may occur a case where an impact produced by the upper impact absorbing member 101 is applied directly to the knee portions H of the pedestrian.
Furthermore, since the knee portions H of the pedestrian are pushed horizontally by an initial impact of the upper impact absorbing member 101, even though lower portions of the leg portions L of the pedestrian are carried upwards by virtue of the difference in rigidity or collapsing amount between the upper and lower impact absorbing members 101, 102 to thereby mitigate the impact, the degree of a damage to the knee portions H may be increased.